The goal of this research is to gain a better understanding of the mechanisms and factors regulating the assembly and secretion of chylomicron (CM) and very low density lipoprotein (VLDL) particles by the rat small intestine. To approach this important question, we will use a unique tool, the hydrophobic surfactant, Pluronic L-81 (L-81). Studies by the principal investigator have demonstrated that unique ability of L-81 to inhibit the formation of certain triglyceride (TG)-rich particles (predominantly CM- sized particles) but not of others (predominantly the VLDL-sized particles), thus providing evidence of the existence of two separate pathways for the formation of intestinal CM- and VLDL-sized particles. The intestinal lymph fistula rat will be used as the in vivo model for the following studies. This model not only yields data regarding the digestion, absorption, and intracellular metabolism of the absorbed lipid, but also enables the investigator to measure directly the amount of lipid transported into lymph. Using the lymph fistula rat, we will study: 1) whether L-81 inhibits the intestinal transport of the TG derived from the glycerophosphate pathway; 2) the formation and transport of CM during the reversal of L-81 inhibition; 3) whether L-81 is less efficient in inhibiting the lymphatic transport of lipid after triolein infusion in the female as opposed to the male rat; 4) the relationship of total lymphatic fatty acid (FA) output to the distribution of absorbed FA between CM and VLDL; 5) the lymphatic apolipoprotein B (apo B) output by electroimmunoassay during lipid absorption as measured by electroimmunoassay; 6) the lipid and protein composition of the large osmiophilic lipid droplets accumulated in the intestinal epithelial cells after feeding triolein plus L-81. The proposed studies are important because they will yield information toward the advancement of our understanding of the mechanism of the assembly of intestinal lipoproteins, a highly important but poorly understood area.